Correct Answer: D. Lunate is dislocated anteriorly but the rest of the carpals remains in position
This option is INCORRECT and therefore the right answer. The statement confuses perilunate dislocation with lunate dislocation—two distinct injuries. In perilunate dislocation, the lunate remains in its normal anatomical position within the lunate fossa of the radius, but the remaining carpal bones (scaphoid, capitate, triquetrum, hamate) dislocate dorsally around it. The lunate itself is NOT anteriorly dislocated in perilunate injury. The option incorrectly describes lunate dislocation (where the lunate alone is displaced anteriorly into the carpal tunnel, compressing the median nerve), not perilunate dislocation. This is a classic NBE trap that conflates two related but mechanistically different wrist injuries. Perilunate dislocation results from high-energy dorsiflexion injuries and is often associated with scaphoid fractures (trans-scaphoid perilunate dislocation). The key discriminator is that in perilunate dislocation, the lunate's position is preserved relative to the radius—it is the perilunar carpal ring that dislocates. Understanding this distinction is critical for diagnosis on plain radiographs and for appropriate surgical management.
Why the other options are wrong
A. Tavernier's manoeuvre is used for closed reduction — This is CORRECT. Tavernier's manoeuvre (also called the Tavernier technique) is a well-established closed reduction method for perilunate dislocation. It involves longitudinal traction, wrist extension, and gentle manipulation to reduce the dorsally displaced carpal bones back into alignment with the lunate. This is a standard orthopedic procedure taught in Indian medical schools and is the first-line approach before considering open reduction if closed reduction fails. B. Lunate remains in position but rest other dislocate dorsally — This is CORRECT and is the defining anatomical feature of perilunate dislocation. The lunate stays in place within the lunate fossa of the radius, while the scaphoid, capitate, and other carpal bones shift dorsally. This distinguishes perilunate dislocation from lunate dislocation, where the lunate itself is displaced. This is the pathognomonic finding on lateral wrist radiographs. C. Involves median nerve injury — This is CORRECT. Median nerve compression and injury are well-documented complications of perilunate dislocation, particularly when the lunate or displaced carpal bones compress the nerve within the carpal tunnel. Acute carpal tunnel syndrome with paresthesias in the median nerve distribution is a recognized presentation. Nerve injury rates vary but are significant enough to warrant careful neurological examination and sometimes urgent decompression.
High-Yield Facts
- Perilunate dislocation: lunate in situ, perilunar carpals dislocate dorsally; lunate dislocation: lunate alone displaced anteriorly into carpal tunnel.
- Trans-scaphoid perilunate dislocation is the most common variant, often missed on initial radiographs—requires CT or MRI for diagnosis.
- Tavernier's manoeuvre (longitudinal traction + extension + gentle reduction) is first-line closed reduction; open reduction via dorsal approach if closed reduction fails.
- Median nerve injury occurs in 25–50% of perilunate dislocations due to compression by displaced carpal bones or swelling.
- Lateral wrist X-ray shows loss of normal carpal alignment (disrupted arc of Gilula); lunate remains aligned with radius in perilunate but not in lunate dislocation.
- High-energy dorsiflexion injury (fall on outstretched wrist, motor vehicle accident) is the typical mechanism in Indian trauma presentations.
Mnemonics
PERI vs LUNATE Dislocation PERIlunate = PERIpheral carpals move (lunate stays put). LUNATE dislocation = LUNATE itself moves (anteriorly into carpal tunnel). Use: When you see 'lunate in place' on X-ray, it's perilunate; when lunate is gone from its fossa, it's lunate dislocation. Tavernier = Traction + Extension + Gentle Turn Traction (longitudinal pull), Extension (wrist dorsiflexion), Gentle manipulation (reduce carpals back). Use: When asked about closed reduction technique for perilunate dislocation, recall Tavernier's three-step approach.
NBE Trap
NBE pairs perilunate and lunate dislocations to trap students who conflate the two. The question asks which statement is INCORRECT about perilunate dislocation, and option D describes lunate dislocation instead—a classic substitution trap that tests whether students truly understand the anatomical distinction between these injuries.
Clinical Pearl
In Indian trauma centers, perilunate dislocations are often initially missed because they are overshadowed by associated fractures (especially scaphoid fractures). Always examine the carpal alignment on lateral wrist X-rays and maintain a high index of suspicion in high-energy wrist injuries; delayed diagnosis leads to chronic instability and post-traumatic arthritis, a common cause of wrist disability in Indian laborers and construction workers.
_Reference: Bailey & Love Ch. 36 (Wrist & Hand Injuries); Rockwood & Green's Fractures in Adults (Wrist Dislocations section)_